Reproduction, reproduction in organisms, reproduction in organisms short notes, asexual reproduction, types of asexual reproduction

   Reproduction   

It is a biological process of continuity of a race in which the grown-up individuals give rise to offspring which is similar to them. Reproduction is an essential phenomenon as it.: - 

(i) Enables continuity of the species.

(ii) Maintains life on the earth. 

(iii) Creates variations among population. The process of reproduction varies in different, organisms, depending on their habitat, internal physiology and several other factors. 

Types of Reproduction: -

Based on whether there is participation of one or two organisms in the process, reproduction can be of following two types 

(i) Asexual reproduction 

(ii) Sexual reproduction.

Asexual Reproduction: -

In asexual reproduction, a single parent is capable of producing offspring. Thus, the offspring are genetically and morphologically identical to one, another and to their parent. These are oftenn referred to as clone. The unit of reproduction is commonly formed from the somatic cells of the parent. Meiosis does not occur in asexual reproduction.

Asexual reproduction is common among single-celled organisms and in plants and animals with relatively simpler body organisation. Cell division itself is a mode of reproduction in protists, e.g. Amoeba and monerans. In bacteria, the parent cell divides into two to give rise to new individuals. 

Types of Asexual Reproduction: -

Types of asexual reproduction are as given below Fission, it can be further classified as 

(i) Binary fission the body of an individual divides into two equal halves. It can be off following types.: -

(a) Simple binary fission When division occurs in any plane, but it is always at right angle to the elongated dividing nucleus, e.g. Amoeba 

(b) Longitudinal binary fission When division occurs along the longitudinal axis, e.g. Euglena, Vorticella. 

(c) Oblique binary fission When division occurs at an angle to the transverse axis, e.g. Corallium, Gonyaulax. 

(d) Transverse binary fission When division occurs along the transverse axis of the individual, e.g., Paramecium diatoms, bacteria, Planaria. 

(ii) Multiple fission the division of the parent body into many daughter organisms, e.g. Plasmodium, Monocytes (all protozoan). 

Budding: -

In budding, an outgrowth or bud develops, grows, constricts at the base and separates from the parent body, e.g. yeast and Hydra. The complex budded condition in which a single organism bears many buds is called torula stage and the process is called torulation.

Sporulation: -

It occurs by tiny, single-celled, thin-walled spores that are extremely resistant to environmental extremes. The spores form new individuals during favorable conditions. 

These are most commonly formed in Monera, Protista, Fungi and Algae. Spores formed can be of following main types: - 

• Pseudopodiospore (with fine pseudopodia) - Amoeba 
• Zoospores (motile and flagellated) - Chlamydomonas and Ulothrix 
• Conidia (non-motile) - Penicillium 
• Sporangiospores (non-motile) -Rhizopus 
• Gemmules (internal buds) - Sponges

Fragmentation: -

It occurs by breaking of the parent body into two or more parts, each of which grows to form an independent individual, e.g. algae like Spirogyra and bryophytes such as Marchantia, Riccia, etc. 

Regeneration: - 

It is a type of asexual reproduction in which the missing part of the organism is repaired by the proliferation of cells, eg. Hydra, Planaria and sponges.

Vegetative Propagation: -

It is the formation of a new plant from vegetative parts like root, stem, leaf, ctc., naturally. The units of vegetative propagation such as runner rhizome, sucker, tuber, offset, bulb, etc. have capability to give rise to new offspring. These structures are known as vegetative propagules. Some artificial methods of vegetative propagation are also used by the farmers like cutting, layering. grafting, etc.

Water hyacinth (scourge of the water bodies or Terror of Bengal) propagates very quickly by vegetative mode and drains out dissolved0, from water bodies.